R is a nested vector of character vectors giving the full path names of the functions or operators in the execution stack. Note that if a function has changed space, its original (home) space is reported, rather than its current one.
In the following, function foo in namespace x has called goo in namespace y. Function goo has then changed space (⎕CS) to namespace z where it has been suspended:
)si [z] y.goo[2]* x.foo[1]
⎕XSI reports the full path name of each function:
⎕xsi #.y.goo #.x.foo
This can be used for example, to edit all functions in the stack, irrespective of the current namespace by typing: ⎕ed ⎕xsi
See also State Indicator .